In a process for detecting a metal plate, the presence of a defect is determined in the metal plate or the position of the defect is determined if present. However, it is more important to obtain quantitative information (e.g., size, contour shape) on the defect, which is key for the evaluation of the health status of the metal plate and the maintenance of the metal plate. With increasingly strict requirements on the safety of the metal plate, there are needs to determine the contour shape of the defect, to image the defect with high precision, and to visualize a detection result of the defect.
Compared with the nondestructive testing technology in the related art, an ultrasonic guided wave has characteristics of low attenuation, far propagation distance, 100% coverage of the thickness of the metal plate by a sound field, ease to adjust the guided wave mode, etc., and the use of a magnetic acoustic array to detect an area surrounded by the array from multiple angles with the ultrasonic guided wave can provide more rich and accurate defect information for high-precision imaging of the defect. However, when the guided wave encounters a strong degree of scattering by the defect, the scattering effect will produce more artifacts in an image of the defect rebuilt by an imaging method with the ultrasonic guided wave in the related art, resulting in blind detection region and seriously affecting the defect location and imaging accuracy of the metal plate. In addition, the shape of an actual defect is very complex, scattering characteristics are varied, and it is difficult to find a unified model to describe the scattering process and extract the scattering characteristics. The above problem is a bottleneck problem that restricts the development of the electromagnetic ultrasonic guided wave detection technology and deteriorates the imaging quality of the defect.